Andy Reid opened training camp saying he was "curious" to see how all the changes to his Eagles team would play out.
He is just days away from getting his first real answers, and they will come against a Green Bay Packers team that finished third in scoring offense and seventh in scoring defense in 2009 and is favored by many to reach the Super Bowl.
"I welcome the challenge," Reid said Wednesday. "I think our football team welcomes the challenge. We know that they're a good football team. People are predicting them to go to the Super Bowl, and rightly so."
With a tumultuous off-season, a grueling training camp, four preseason games, and a final weekend of roster maneuvering behind them, the Eagles on Wednesday held their first full-length practice focused on the regular season and the Packers.
There are certainly easier games the Eagles could open with, given the rest of the teams on their schedule.
"That's not Philly style, though," quarterback Kevin Kolb said with a laugh. "We know they're a great team and I like that. We're going out and we're testing ourselves right off the bat."
With no regular-season games to use as reference, the one word Reid repeated most often throughout his Wednesday news conference was unknown.
Will the Eagles' offensive line be able to handle the Packers' pass rush? How will center Jamaal Jackson hold up through a full four quarters of play? Will the starting offense finish inside the red zone?
How will a reshaped defense handle a team that put up nearly 29 points per game in 2009? And a rising quarterback - Aaron Rodgers - who threw more touchdowns last year than anyone except Drew Brees, Brett Favre, and Peyton Manning?
There will be few available excuses if the Eagles fall short: Every player on their active roster practiced Wednesday and should be ready Sunday, a rarity coming out of training camp.
It will still be another three days of practice and game-planning and waiting, but the purpose of all the grinding that has come since the end of last season is in sight for the young Eagles as Sunday nears.
"I think we're all excited to get on with it," Reid said. "It's unknown territory, but that's OK. That's the challenge of it."
Watching the center. Reid will be keeping a close eye on Jackson on Sunday and how he endures his first four quarters of competition since suffering a torn left anterior cruciate ligament Dec. 27.
Reid and Jackson said doctors have cleared the center's knee medically - Jackson said he received a doctor's blessing to return to practice as early as July - but that still leaves open the question of how effective the center can be. Reid, asked about his comfort level with Jackson, acknowledged that the center's play was an "unknown" heading into week one.
"I feel comfortable with him, he feels comfortable, and the doctors feel comfortable, but I can't tell you I'm not going to keep a close eye on him. I will do that," Reid said.
Asked whether Jackson was back to the same physical level as before the injury, Reid said, "That's some of the unknown. We've just got to see how he does and sustains throughout the game."
Jackson will face a tough early test, going against a defense that will line up 6-foot-2, 337-pound nose tackle B.J. Raji over center.
Jackson, who is wearing a brace on the repaired knee, said he expected to participate fully in practice this week, just as he would for any other game. He said doctors have assured him that the knee was no more vulnerable to injury than any other knee.
"The knee is healthy enough to withstand physical contact," he said.
As to whether that means his quickness and power are back, Jackson thought for a moment to consider the question. The biggest test, he said, is going a full game against NFL defenders. So far, he has been through only practices.
"It feels good. It's just the endurance part of it," he said. "I haven't had a chance to do any preseason. Four quarters, the first game, there's going to be a lot of energy a lot of people are going to be amped up, so hopefully, emotionally, I don't drain myself."